A polyester resin has been widely used in the fields of the packing materials, the articles and the films, and is one of the environment-friendly plastics which have no endocrine disruptors. Recently, regarding the polycarbonate which has been used as the heat-resisting container for food, harmfulness of bisphenol-A to the human being has been revealed, and, a need for the environment-friendly transparent and heat-resisting polyester resin has increased. The polyester resin which is copolymerized with at least two glycol or dicarboxylic acid components has been commercially widely used to improve a moldability thereof and to remove a crystallinity thereof. In the case of homopolyester which is polymerized with only terephthalic acid and ethylene glycol, material properties and heat-resistance thereof can be enhanced through a stretching-induced crystallization and heat-setting. However, there are limitations on application and enhancement of heat-resistance. In the case of polyester which is copolymerized with at least two glycol or terephthalic acid components, there is a disadvantage that it is difficult to enhance heat-resistance thereof by stretching or crystallize process. As another method to enhance heat-resistance of the polyester, it is known that the isosorbide (1,4:3,6-dianhydroglucitol) which is an environment-friendly diol compound derived from starch, is used as one of monomers.
U.S. Pat. No. 5,959,066 discloses a method for preparing polyester having the intrinsic viscosity of 0.35 dl/g or more by melt polymerization using terephthalic acid or dimethylterephthalate and various diols comprising isosorbide. The polyester resin having the intrinsic viscosity of 0.35 dl/g or more is used for optical products and coating, and the polyester resin having the intrinsic viscosity of 0.4 dl/g or more is used for CD, and the polyester resin having the intrinsic viscosity of 0.5 dl/g or more can be used for a bottle, a film, a sheet and injection molding. Moreover, U.S. Pat. No. 6,063,464 discloses a method for preparing the polyester having the intrinsic viscosity of 0.15 dl/g or more by melt polymerization using the glycol components comprising isosorbide. And, U.S. Pat. No. 6,656,577, U.S. Pat. No. 6,359,070, U.S. Pat. No. 6,140,422 and so on disclose a method for preparing the copolymerized polyester resin using the glycol components comprising isosorbide.
The above patents disclose a method for polymerizing polyester using common catalysts with all of acids and diols comprising isosorbide, however, it may cause yellowing during the synthesis or forming of polyester, therefore, a composition for color stability (transparency) is needed to be used for normal plastics.